Mysterious coolant leak? Check your overflow tank cap.

My radiator has been losing small amounts of coolant on long road trips (500+ miles). The truck runs exceptionally well so this problem really bothered me.

Visually, I checked for leaks everywhere multiple times. I found nothing.

I pressure tested the coolant system multiple times. I observed perfect results each time.

I replaced the radiator cap. Coolant kept disappearing.

I replaced the coolant line to my IAC. Coolant kept disappearing.

I left red meat on my balcony as an offering to the Toyota Tacoma gods. Coolant kept disappearing but my beard got more thick.

Finally, I realized my error. The radiator overflow line was installed incorrectly on the overflow tank cap.

Observe below. If the radiator overflow line is installed incorrectly, coolant will drip into the overflow tank but will not get sucked back into the radiator. More, air might get introduced into the radiator. Your radiator overflow and tank overflow lines should be configured as shown in the below photos.

Learn from my stupidity.